Fix crashes when calling Array.sort with imperfect sort functions

We can't use std::sort to implement Array.sort. The reason is that
std::sort expects a conformant compare function, and can do weird
things (esp. crash) when the sort function isn't conformant.

Falling back to qSort is not possible, as the method has been
deprecated. So add a copy of the qSort implementation here, and
use that one instead.

Fix the sortint test in tst_qqmlecmascript to have a consistent
sort function for strings, as the result of calling sort is
otherwise undefined according to the ecma standard.

Task-number: QTBUG-39072
Change-Id: I0602b3aa1ffa4de5006da58396f166805cf4a5e2
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>